CONJUGATION IN UNICELLULAR FORMS 



169 



rapid multiplication of the nucleus followed by a corresponding divi- 

 sion of the cell-body to form "spores," which remain for a time 

 closely aggregated before their liberation. The resemblance of this 

 process to the fertilization and subsequent cleavage of the ovum is 

 particularly striking. 



The conjugation of unicellular plants shows some interesting 



D 



Fig. 85. — Conjugation of Spirogyra. [OVERTON.] 

 A. Union of the conjugating cells {S. communis). D. The typical, though not invariable, 

 mode of fusion in 5. Weberi ; the chromatophore of the " female " cell breaks in the middle, 

 while that of the " male " cell passes into the interval. C. The resulting zygospore filled with 

 pryrenoids, before union of the nuclei. D. Zygospore after fusion of the nuclei and formation 

 of the membrane. 



features. Here the conjugating cells completely fuse to form a 

 "zygospore" (Figs. 85, 99), which as a rule becomes surrounded by 

 a thick membrane, and, unlike the animal conjugate, may long remain 

 in a quiescent state before division. Not only do the nuclei unite, 

 but in many cases the plastids also (chromatophores). In Spirogyra 

 some interesting variations in this regard have been observed. In 

 some species De Bary has observed that the long band-shaped chro- 

 matophores unite end to end so that in the zygote the paternal and 



